Positron emission tomography (PET) technology has been widely used in clinical examination and disease diagnosis in recent years. A wide-field PET device including a plurality of axial PET units has a wide field of view and may be used to scan all or part of an object. Image reconstruction is a key technology in the field of PET. However, traditional reconstruction techniques may be unable to simultaneously reconstruct images of different portions of a scanned object based on different reconstruction parameters. Additional, a traditional reconstruction technique may be complex and need a large amount of calculation resources. Thus, it may be desirable to develop an image reconstruction method and system that may solve the above mentioned problems.